The most common source of electrical lighting has been the incandescent filament lamp because of several beneficial characteristics: Low manufacturing cost; Availability in a wide variety of light outputs; Availability in a wide variety of operating voltages for direct operation from various power sources with no intervening power supply; Operation across wide ranges of ambient temperatures; Easily adjustable light output using low cost electronic dimmers; Generally no or very limited flicker in output at commercially utilized power line frequencies; and Relatively benign disposal characteristics. Within reasonable ranges, various output lamps can be used in the same fixture providing user capable lighting flexibility. Operation of lamps is independent of whether power source is AC or DC. Relatively benign operating characteristics present an easy load to power sources. Continuous spectrum output results in a High Color Rendering Index (CRI) for accurate color reproduction of illuminated objects.
The incandescent lamp has substantial limitations that are increasing pressure to migrate to other technologies including: Relatively low conversion of input power to light output commonly referred to as lumens per watt; The energy cost of the lamp over its life outweighs the low cost of the lamp; High heat production in relationship to light output; Most lamps present a burn risk if they are handled while operating; Relatively fragile to shock; Change in color temperature with change in input voltage; Relatively short life for lamps with even reasonable light output; and Very short life for overvoltage conditions. Lamp life decreases with the 12th power of voltage. For normal lamps light output drops with age as the filament material transfers to the envelope. Lamps with longer life such as tungsten halogen have high starting current and operate at high pressures presenting an explosion hazard. Tungsten halogen lamps require special handling to prevent damage by contaminants while lamping.
Other technologies have been investigated and used for light production with the primary goal to increase efficiency. The most common include fluorescent lamps, and high and low pressure gas discharge lamps including metal additive types and most recently Light Emitting Diodes (LED). Of the alternative technologies, fluorescent lighting has seen the widest acceptance in general residential and industrial lighting. Advantages of this technology include: Higher efficiency; Relatively long life; and Relatively low lamp cost. Disadvantages of fluorescent lighting include: Lamps cannot be operated directly off common power sources without intervening power supplies (ballasts); Dimming cannot be done with common low cost dimmers; Some degree of flicker exists at normal line frequencies; Common ballasts waste power and can cause noise; More efficient high frequency ballasts are more expensive; Cold weather performance is poor without special lamps and ballasts; The lamps are very fragile; Except for very expensive lamps, the CRI is only fair; and Most lamps have a warm up time to reach full light output. Lamps contain mercury and phosphors which are hazardous materials and require special disposal to prevent environmental problems.
Attempts to directly replace incandescent lamps in the existing incandescent fixtures with Compact Fluorescent Lamps (CFL) are only partially successful because each lamp requires individual ballast and may be too large to fit the fixture. These lamps have severely shortened life if dimming is attempted and the efficiency is lower than permanent fluorescent fixtures with more sophisticated ballasts. Their cost is high because each lamp must have a dedicated ballast. When the lamp fails, the ballast is discarded along with the lamp.
Although still a relative newcomer to lighting technology, the LED has the greatest potential to become the standard type of light source for the majority of residential and commercial lighting applications. The characteristics that make the LED a strong contender include: Very high conversion efficiency of electricity to light; Very long life; Immunity to most shock and other physical hazards; Relatively cool operation; CRI that is better than other high efficiency types; Constant color temperature with dimming; Immediate light output with no warm up time; and Low up front cost if properly implemented.
The disadvantages of LED light sources include: Cannot be used directly off existing power lines; DC only operation requires some form of conversion of AC supplies to DC; Generally require current limiting as they are more a current responsive device than voltage responsive; and they work more efficiently in series configurations rather than parallel which is the norm for existing lighting setups. Series operation has the problem that if one segment of the series string fails, the whole string fails.
Current attempts to use LED lighting in existing lighting fixtures requires that each lamp have a built in power supply which adds considerable cost and size, reduces efficiency and like CFL lamps is discarded when the lamp is replaced. Operation with existing simple solid state dimmers may not be possible or satisfactory.